Activation of nickel battery plates

ABSTRACT

Electrolytic process for activating essentially solid nickel surfaces, e.g., nickel foil, for use as the positive electrodes in alkaline storage batteries. The electrolyte contains in solution a nickel salt, ammonia and an ammonium salt having the same anion as the nickel salt.

United States Patent Turner et al.

[4 1 July 15,1975

ACTIVATION OF NICKEL BATTERY PLATES Inventors: Trevor S. Turner, Kidderminster;

John E. Whittle, Sutton Coldfield, both of England Assignee: The International Nickel Company,

Inc., New York, NY.

Filed: Mar. 2, 1973 Appl. No.: 337,586

Foreign Application Priority Data Jan. 20, 1970 United Kingdom ..l240445 Related U.S. Application Data Continuation of Ser, No. 107,422, Jan. 18, 1971.

U.S. Cl. 136/29; 204/56 R Int. Cl. HOlm 35/00 Field of Search 136/28, 29, 154, 155, 76;

References Cited UNITED STATES PATENTS l/l961 Fleischer 136/29 3,146,130 8/1964 Kroger et al 136/34 3,269,864 8/1966 Ackermann et al. 136/29 3,335,033 8/1967 Kober 136/29 3,579,383 5/1971 Turner 136/76 Primary Examiner-John l-l. Mack Assistant Examinerl-l. A. Feeley Attorney, Agent, or Firm-Francis J. Mulligan, Jr.; Ewan C. MacQueen 2 Claims, No Drawings 1 ACTIVATION OF NICKEL BATTERY PLATES This application is a continuation of our copending U.S. application Ser. No. 107,422 filed .lani 18, 1971.

The invention is directed to the preparation-of positive electrodes suitable for use in alkaline storage batteries.

Activated sintered nickel plates have found wide application as positive electrodes in alkaline storage batteries. However, because sintered nickel plates are porous and have diffused bonds, they are not characterized by a strength and ductility comparable to that of a dense, thin sheet material. It has been recognized that a thin, activated metal, foil, for example, nickel foil, is potentially a superior positive electrode material because, by employing such foil, the final size of a storage battery may be substantially reduced. Further, batteries having activated foil electrodes are able to produce very high discharge rates for short periods at a substantiallly constant potential. This property is in contradistinction to the discharge of a capacitor which, though capable of a high discharge rate, exhibits a potential which decays exponentially with time.

In the Turner U.S. Pat. No. 3,579,383, patented May 18, 1971, there is described a process for activating nickel foil or sheet in order to render it suitable for use as an electrode in an alkaline storage battery. In this process the foil or sheet is anodically treated in an aqueous electrolyte containing a nickel ammine complex, the so-called active mass being deposited from the electrolyte onto the foil or sheet which constitutes the anode in the electrolytic process. The active mass deposited is the black form NiO(Ol-1), and is substantially adherent to the solid nickel surface. The nickel ammine complex is formed by the addition of ammonia to an aqueous solution of a nickel salt which may be nickel nitrate, nickel acetate, nickel sulfate or nickel chloride. The process is distinguished from the slower prior art processes for foil activation which entirely rely on corrosion of the foil to provide the battery active mass.

In the above-mentioned patent, nickel nitrate is pointed out as a most advantageous nickel salt for use in the electrolyte. Further, the ratio of ammonia to nickel (gram-molecules to gram-ions) in the electrolyte is described therein as being maintained at a value between 0.1 to 3 when the current density lies in the advantageous range of from 10 to 50 mA/cm (milliamperes per square centimeter). However, current density may fall in the range from 0.1 to 1000 mA/cm or, more desirably, from 10 to 500 mA/cm While the temperature of the electrolyte is maintained advantageously in the range from about 20C. to about 30C. and should not exceed 35C., the process is operable below room temperature, even as low as C. The treatment may be conducted for periods ranging from as short as minutes to 2 or 3 hours or more. High solution concentrations of nickel nitrate can be obtained. Desirably, the Ni(NO .6l-l 0 concentration is kept above 100 g/l. (grams per liter) and up to the saturation point, e.g., 800 to 1000 g/l.

The process described above has been successfully employed to activate nickel foil electrodes, but since, in practice, the electrolytes are maintained in use for long periods of time for activating large quantities of foil or sheet, it is found that in the course of time they tend to become unstable, and the amount of active mass formed in a given time tends to vary.

It has now been discovered that the stability of the electrolyte, and the uniformity of the amount of active mass formed, are much improved by the addition to the electrolyte of an appropriate ammonium salt.

lt is an object of the inventionto provide in the manufacture of plates for alkaline batteries, an anodic deposition process for activating. solid nickel surfaces wherein the deposition of battery active mass is carried out in a nickel-ammine electrolyte stabilized by an ammonium salt.

It is a further object of the invention to'provide a stable electrolyte containing a nickel-ammine complex which is suitable for the activation of solid nickel surfaces by the addition to the electrolyte of an ammonium salt that hasthe same anion as the nickel salt from which the complex was formed. 1

Other objects and advantages will become apparent in the following description.

Generally speaking, the electrolyte in accordance with this invention is an aqueous solution of a nickel salt, ammonia and an ammonium salt that has the same anion as the nickel salt, the ammonium salt being present in an amount such that the ratio of the molar concentration of the ammonium salt to that of the nickel salt is at least 0.1:1, but does not exceed 3:1. At higher ratios the nickel anode is corroded to an undesirable extent. A suitable ratio is from 1:1 to 15:1.

Advantageously, the two salts used in preparing the electrolyte are nickel nitrate and ammonium nitrate. The ratio of ammonia to nickel (gram-molecules to gram-ions) in the electrolyte is beneficially from 0.1 to 3, as described in the Turner U.S. Pat. No. 3,579,383, and the temperature of the electrolyte and the current density employed also fall in the ranges set forth in that application.

Examples of electrolytes according to the invention, the concentrations of the salts and ammonia being given in gram-molecules, are set forth in the following Table.

Each electrolyte was kept for two months and then examined. Electrolytes 1 to 3 showed a slight precipitate, amounting to 1% by volume of the solution in Electrolyte 1, less than 1% in Electrolyte 2 and very slight in Electrolyte 3. Electrolytes 4 to 6 showed very slight turbidity. Electrolytes 7 to 9 did not even show turbidity, but in use tended to corrode nickel anodes slightly. 1n contrast, in an electrolyte without the stabilizing addition which contained 825 g/l. (grams per liter) of Ni(NO .6l-l O and sufficient 0.880 ammonia to give a ratio of Nl-l /Ni' equal to 2.75 (Example V of the Turner U.S. Pat. No. 3,579,383), 30% of the solution by volume had precipitated after 2 months.

The capacity of each of the nine electrolytes according to the invention for the production of active mass was evaluated by ascertaining the gain in weight of a circular nickel sheet 3.2 mm. thick and of total area 6 cm when immersed as the anode in the electrolyte through which a current was passed for 2 /2 hours at an anode current density of 18 mA/cm, the temperature being 20C. The gains in weight are shown in the Table above.

It will be understood that the essentially solid nickel surfaces such as nickel foil which are activated in accordance with this invention may be perforated to a considerable degree, e.g., up to l% hole area or more.

The present invention thus provides a means for stabilizing nickel-ammine solutions used in activating battery plates so that it becomes practical to use such solutions for prolonged periods in activating large quantities of foil or sheet.

Although the present invention has been described in conjuction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of 4 the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A stabilized electrolyte for activating essentially solid nickel surfaces for use as positive electrodes in alkaline batteries comprising an aqueous solution made by combining water, nickel nitrate, ammonium nitrate and ammonia to contain nickel in an amount equivalent to at least grams per liter of ,nickel nitrate measured as the hexahydrate, the combination of ingredients being such that the ratio of the molar concentration of ammonium nitrate to nickelnitrate is about 0.1

to about 3, the ratio to nickel nitrate is about 0.1 to I about 3, the ratio of gram molar of ammonia to gram ions of nickel is about 0.1 to about 3 with the balance of the composition being water.

2. The electrolyte of claim 1, in which the ratio of molar. concentration of ammonium nitrate to that of nickel nitrate is about 1 to about 1.5. 

1. A STABILIZED ELECTROLYTE FOR ACTIVATING ESSENTIALLY SOLID NICKEL SURFACES FOR USE AS POSITIVE ELECTRODES IN ALKALINE BATTERIES COMPRISING AN AQUEOUS SOLUTION MADE BY COMBINING WATER, NICKEL NITRATE, AMMONIUM NITRATE AND AMMONIA TO CONTAIN NICKEL IN AN AMOUNT EQUIVALENT TO AT LEAST 100 GRAMS PR LITER OF NICKEL NITRATE MEASURED AS THE HEXAHYDRATE, THE COMBINATION OF INGREDIENTS BEING SUCH THAT THE RATIO OF THE MOLAR CONCENTRATION OF AMMONIUM NITRATE TO NICKEL NITRATE IS ABOUT 0.1 TO ABOUT 3, THE RATIO TO NICKEL NITRATE IS ABOUT 0.1 TO ABOUT
 2. The electrolyte of claim 1, in which the ratio of molar concentration of ammonium nitrate to that of nickel nitrate is about 1 to about 1.5.
 3. THE RATIO OF GRAM MOLAR OF AMMONIA TO GRAM IONS OF NICKEL IS ABOUT 0.1 TO ABOUT 3 WITH THE BALANCE OF THE COMPOSITION BEING WATER. 